/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.ejb.access;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import javax.ejb.CreateException;
import javax.ejb.EJBLocalHome;
import javax.ejb.EJBLocalObject;
import javax.naming.NamingException;

import org.aopalliance.intercept.MethodInvocation;

import org.springframework.lang.Nullable;

/**
 * Invoker for a local Stateless Session Bean.
 * Designed for EJB 2.x, but works for EJB 3 Session Beans as well.
 *
 * <p>Caches the home object, since a local EJB home can never go stale.
 * See {@link org.springframework.jndi.JndiObjectLocator} for info on
 * how to specify the JNDI location of the target EJB.
 *
 * <p>In a bean container, this class is normally best used as a singleton. However,
 * if that bean container pre-instantiates singletons (as do the XML ApplicationContext
 * variants) you may have a problem if the bean container is loaded before the EJB
 * container loads the target EJB. That is because by default the JNDI lookup will be
 * performed in the init method of this class and cached, but the EJB will not have been
 * bound at the target location yet. The best solution is to set the lookupHomeOnStartup
 * property to false, in which case the home will be fetched on first access to the EJB.
 * (This flag is only true by default for backwards compatibility reasons).
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see AbstractSlsbInvokerInterceptor#setLookupHomeOnStartup
 * @see AbstractSlsbInvokerInterceptor#setCacheHome
 */
public class LocalSlsbInvokerInterceptor extends AbstractSlsbInvokerInterceptor {

    private volatile boolean homeAsComponent = false;


    /**
     * This implementation "creates" a new EJB instance for each invocation.
     * Can be overridden for custom invocation strategies.
     * <p>Alternatively, override {@link #getSessionBeanInstance} and
     * {@link #releaseSessionBeanInstance} to change EJB instance creation,
     * for example to hold a single shared EJB instance.
     */
    @Override
    @Nullable
    public Object invokeInContext(MethodInvocation invocation) throws Throwable {
        Object ejb = null;
        try {
            ejb = getSessionBeanInstance();
            Method method = invocation.getMethod();
            if (method.getDeclaringClass().isInstance(ejb)) {
                // directly implemented
                return method.invoke(ejb, invocation.getArguments());
            } else {
                // not directly implemented
                Method ejbMethod = ejb.getClass().getMethod(method.getName(), method.getParameterTypes());
                return ejbMethod.invoke(ejb, invocation.getArguments());
            }
        } catch (InvocationTargetException ex) {
            Throwable targetEx = ex.getTargetException();
            if (logger.isDebugEnabled()) {
                logger.debug("Method of local EJB [" + getJndiName() + "] threw exception", targetEx);
            }
            if (targetEx instanceof CreateException) {
                throw new EjbAccessException("Could not create local EJB [" + getJndiName() + "]", targetEx);
            } else {
                throw targetEx;
            }
        } catch (NamingException ex) {
            throw new EjbAccessException("Failed to locate local EJB [" + getJndiName() + "]", ex);
        } catch (IllegalAccessException ex) {
            throw new EjbAccessException("Could not access method [" + invocation.getMethod().getName() +
                    "] of local EJB [" + getJndiName() + "]", ex);
        } finally {
            if (ejb instanceof EJBLocalObject) {
                releaseSessionBeanInstance((EJBLocalObject) ejb);
            }
        }
    }

    /**
     * Check for EJB3-style home object that serves as EJB component directly.
     */
    @Override
    protected Method getCreateMethod(Object home) throws EjbAccessException {
        if (this.homeAsComponent) {
            return null;
        }
        if (!(home instanceof EJBLocalHome)) {
            // An EJB3 Session Bean...
            this.homeAsComponent = true;
            return null;
        }
        return super.getCreateMethod(home);
    }

    /**
     * Return an EJB instance to delegate the call to.
     * Default implementation delegates to newSessionBeanInstance.
     *
     * @throws NamingException           if thrown by JNDI
     * @throws InvocationTargetException if thrown by the create method
     * @see #newSessionBeanInstance
     */
    protected Object getSessionBeanInstance() throws NamingException, InvocationTargetException {
        return newSessionBeanInstance();
    }

    /**
     * Release the given EJB instance.
     * Default implementation delegates to removeSessionBeanInstance.
     *
     * @param ejb the EJB instance to release
     * @see #removeSessionBeanInstance
     */
    protected void releaseSessionBeanInstance(EJBLocalObject ejb) {
        removeSessionBeanInstance(ejb);
    }

    /**
     * Return a new instance of the stateless session bean.
     * Can be overridden to change the algorithm.
     *
     * @throws NamingException           if thrown by JNDI
     * @throws InvocationTargetException if thrown by the create method
     * @see #create
     */
    protected Object newSessionBeanInstance() throws NamingException, InvocationTargetException {
        if (logger.isDebugEnabled()) {
            logger.debug("Trying to create reference to local EJB");
        }
        Object ejbInstance = create();
        if (logger.isDebugEnabled()) {
            logger.debug("Obtained reference to local EJB: " + ejbInstance);
        }
        return ejbInstance;
    }

    /**
     * Remove the given EJB instance.
     *
     * @param ejb the EJB instance to remove
     * @see javax.ejb.EJBLocalObject#remove()
     */
    protected void removeSessionBeanInstance(@Nullable EJBLocalObject ejb) {
        if (ejb != null && !this.homeAsComponent) {
            try {
                ejb.remove();
            } catch (Throwable ex) {
                logger.warn("Could not invoke 'remove' on local EJB proxy", ex);
            }
        }
    }

}
